Simplify to lowest terms. $\dfrac{21}{56}$
Explanation: What is the greatest common factor (GCD) of 21 and 56? $21 = 3\cdot7$ $56 = 2\cdot2\cdot2\cdot7$ $\mbox{GCD}(21, 56) = 7$ $\dfrac{21}{56} = \dfrac{3 \cdot 7}{ 8\cdot 7}$ $\hphantom{\dfrac{21}{56}} = \dfrac{3}{8} \cdot \dfrac{7}{7}$ $\hphantom{\dfrac{21}{56}} = \dfrac{3}{8} \cdot 1$ $\hphantom{\dfrac{21}{56}} = \dfrac{3}{8}$